In U.S. Pat. No. 5,404,967 entitled EXTRUDING DEVICE which issued Apr. 11, 1995 and which names the same inventor, the contents of which are incorporated herein by reference, there is disclosed and claimed an extruding device used to extrude grease and other fluids, typically to male grease fittings which provide lubrication for moving parts. The extruding device according to the aforementioned United States patent teaches two pistons, each piston being reciprocal in a respective passageway and being movable simultaneously in the same direction to discharge fluid from the passageways in which they move.
The two pistons reciprocated in their respective passageways. The two pistons were joined to a piston mounting block with a drive pin extending therefrom. The drive pin fitted into a drive groove formed in a rotating cam. As the cam rotated about an axis, the drive block and, therefore, the attached pistons reciprocated.
While the system worked reasonably well, premature failure of the drive pin was noted. It is fairly well determined that the source of the failure lay in the high loading on the pistons caused by the grease in the fluid passageways in which the pistons moved. Because this loading was variable and ranged through a relatively large quantity of forces being exerted on the pistons and likewise because the drive pin was a cantilever type member extending from the mounting block, the forces were sufficient to cause failure of the drive pin thereby causing a prematurely short life of the drive pin and failure of the entire system.
Yet a further disadvantage of the previous system is that the forces were highest, expectedly so, on the power stroke of the extruding operation. Thus, if failure was anticipated, it would be logical to expect it to occur on the power stroke. The design of the drive system of the extruding apparatus according to the '967 patent did nothing to assist a reduction in these forces and a more even application of force throughout the power and suction strokes of the system.